The present invention relates to a reader-printer having a device for rotating an image of microfilm on a projection surface.
The frames on a microfilm are in a vertical or horizontal position relative to the film, while information is recorded in the frame in a vertical or horizontal position relative to the frame. If images on the microfilm are projected with the film in a definite position, it is likely that the image will be projected in an inappropriate orientation. For example, information projected as oriented horizontally in the reader mode is almost impossible to read. Further if the orientation in which the frame is projected is not in coincidence with the orientation of the copy paper in the printer mode, an incomplete copy will be obtained. These objections can be eliminated by rotating the microfilm, but the device for holding the film must then be rotated. This requires a comlex arrangement.
U.S. Pat. No. 3,907,418 discloses an arrangement wherein the film image to be projected is rotated on a plane of projection by a prism. The prism employed is a trapezoidal prism, i.e., Dove prism, and is disposed at the light emergent side of a projection lens rotatably about the optical axis of the lens. The rotation of the prism rotates the image through twice the angle of rotation thereof. The arrangement of U.S. Pat. No. 3,907,418 is based on the assumption that although the frames are directed vertically or horizontally relative to the film, information is recorded in the frames in an upright position relative to the film, and is adapted to selectively determine whether the prism in an orientation in the reader mode is to be rotated through 45 degrees in operative relation with the change of mode to the printer mode, such that the prism is rotated only when the direction of the frame is not in coincidence with the orientation of the paper in the printer mode.
However, the disclosed technique still requires the user's manipulation and has yet to be improved in the ease of use.
The technique has another problem in that the prism wherein the incidence optical axis coincides with the emergence optical axis is large-sized, whereas use of a small prism for compacting the apparatus involves deviation between the incidence optical axis and the emergence optical axis to result in the deviation of the projected image on copy paper.